FLOOD03098

• County: Larimer
• Community: Fort Collins
• Stream Name: Cooper Slough, Boxelder Creek
• Basin: South Platte
• Title: Master Drainageway Planning Study
• Date: 8/1/1981
• Prepared For: Larimer County
• Prepared By: Simons Li & Associates Inc.
• Floodplain - Doc Type: Floodplain Report/Masterplan

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The assistance and cooperation in supplying information and data of the

agenci~s. and organizations listed below are appreciated and gratefully

acknowledged:

USDA Soil Conservation Service

Colorado State 'Department of Highways

Colorado Water Conservation Board

Larimer County Planning Department

Larimer County Data Processing Department

City of Fort Collins, Colorado

Several of the irrigation ditch companies owning and operating water systems

in the study area were especially helpful. The following companies were

included:

Larimer and Weld Reservoir company

Water Supply and Storage Company

Lake Canal Company

Cache la Poudre Reservoir Company

Our thanks and appreciation are extended to these companies for their coopera-

tion and information.

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Report Acquisition

Copies of this report are available for public distribution, for a nomi-

nal fee, at the offices listed below. A "Technical Addendwn" to this report

is also available for review at the same offices; however, it has not been

published in sufficient quantities for public distribution. The "Technical

Addendwn" includes all pertinent data and calculations used in this report.

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Larimer County Planning Department
Larimer County Courthouse
PO Box 1190
Fort Collins, CO 80522

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Engineering Service Department
City of Fort Collins
PO Box 580
Fort Collins, CO 80522

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Colorado Water Conservation Board
823 State Centennial Building
1313 Sherman Street
Denver, CO 80203

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Related Studies

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Mapping and Surveying
Topographic mapping for this study was furnished by Larimer County,
Colorado, and prepared by photogrammetric methods by R & D Aerographics of
Loveland, Colorado. The scale is 111 :;: 100', and the contour interval is two
feet. Administrative maps at a scale of 111 = 100. have been prepared and are
available at the Larimer County Planning Department, Colorado. The floodplain
maps printed in this report are reduced to a scale of 1" :;: ::$00' for easy
presentation.
Field surveys were completed by Simons, Li & Associates, Inc. to supple-
ment the topographic mapping as required. Channel cross sections were taken
on Cooper Slough along a one-half mile reach north of Vine Drive and the
reach between State Highway Bridge 14 and Cache la poudre Reservoir inlet.
Spot elevations were taken at each roadway and railroad crossing, and loca-
tions where elevations were critical to the hydraulic computations. In
general, field information'was consistent with the topographic mapping.

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A watershed work plan for Boxelder Creek was prepared by the Soil

Conservation Service (SCS) in February 1971 (reference 1) and April 1973

(reference 2). In the first report, the 100-year floodplain was delineated

starting near Wellington and continuing to the confluence with the Cache 1a

poudre River. That report recommended the construction of five floodwater

detention structures. A report detailing the flooded area from a potential

structural failure is defined in reference 3. The hydrologic and hydraulic

analyses in this report were prepared considering the effects of five flood-

water detention structures that, at present, are either completed or under

construction. Floodplain studies were made in 1970 and 1978 (references 4

and 5).

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The floodplain defined in this study for Boxelder Creek was limited to

the area downstream of Willox Lane. More detailed hydrologic and hydraulic

analyses were performed for this area which reflect existing (1980) and deve-

loped field conditions. The results of this report supercede those obtained

in earlier reports. Additional studies by SLA associated with this project

are described in references 6 and 7. The results of these two studies were

adopted for this study.

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4

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